An Implementable Channel and CFO Estimation Scheme for IEEE 802.22-Based Radio Equipment

The IEEE 802.22, which has been standardized as a fixed communication system for a regional area network in the TV white spaces (TVWS), is expected for a backbone network in developing countries where a relatively large amount of the TVWS still exists. On the other hand, significant channel variations in the frequency domain are induced in such a wide area network because of a long- delay multi-path fading. Also, a carrier frequency offset (CFO) causes further channel variations in the time domain. In general, these channel variations are mainly compensated by the linear interpolating (and extrapolating) between reference pilot subcarrier signals. However, the number of symbols are flexible and there are some cases that cannot ensure two pilot subcarriers in the DS subframes based on the IEEE 802.22 standard. In this paper, the authors propose a simplified channel and CFO estimation scheme that can estimate channel variations symbol by symbol with using a frame preamble and several pilot subcarriers in each symbol. It was confirmed by computer simulation that an IEEE 802.22- required BER of less than 2x10^-4 can be achieved in all modulations with a CFO of +67 Hz that is defined as a maximum CFO for a signal bandwidth of 6 MHz in the IEEE 802.22 standard. In the experiment, measured BER performance indicates the same trend as the calculated BER performance, and a BER of less than 2x10^-4 can be achieved in QPSK and 16QAM. From these results, the proposed estimation scheme can be used in the long-delay multi-path fading environment.